Electrostatic clamping arrangements are often used to hold a workpiece being processed at pressures below ambient pressure—i.e., in a vacuum environment. Such processes may include, but are not limited to, chemical and physical material deposition, etching and ion implantation. In many cases, the processes are carried out as part of an overall process of fabricating an electronic product such as an integrated circuit or a display element. A variety of workpieces may thus be involved and include electrically conducting workpieces (e.g., thin sheets of metal, carbon, or other electrically conductive material) and electrically semiconducting workpieces (e.g., silicon wafers on which integrated circuit elements are being formed) or insulating workpieces (e.g., glass substrate portions of an optical display).
In U.S. Pat. No. 6,781,812 Fuwa et al. describe an electrostatic chuck in which the electrodes comprise interleaved spiral conductors electrically insulated from each other and from a substrate. When an electric field having a high rate of spatial change is established between the two conductors, a gradient force acts on an adjacent workpiece and clamps it to the substrate regardless of whether it is electrically insulating or conducting. Fuwa et al. do not teach the use of a bifilar conductor to avoid generating extraneous magnetic fields at the working surface of the workpiece, nor do they teach the use of their spiral structures as resistance heaters.
In many of the processes for which electrostatic clamping is used, one needs to consider heat transfer between the workpiece and a platen or other supporting surface to which the workpiece is clamped. Resistance heating elements are often disposed in or on a substrate in order to heat the workpiece to a desired initial temperature for the process. In addition, because many of the processes (such as sputtering or ion implantation) involve depositing significant energy on the workpiece, provision is often made to prevent overheating by transferring heat to the substrate. In some embodiments, this transfer process involves providing grooves in an otherwise flat substrate and flowing a gas, such as hydrogen or helium, through the grooves.